Ceramics have been used as parts of machines which are exposed to high temperature because of their superior heat-resisting properties, and they are expected to be similarly applied in various fields in the future. However, in the case of, for example, an oxygen sensor utilizing a solid ceramic semiconductor, it is necessary to bond a ceramic member to an electrically conductive metal wire in a body as a combination, because the measurement of the oxygen requires the conductance of electricity. In such a bonded material wherein a ceramic member and a metal member are bonded in a body, a strain is caused between the ceramic member and the metal member when variations of temperatures are great under the circumstances of use, because of differing coefficients of thermal expansion (at a temperature of from room temperature to 300.degree. C.), as shown in Table 1.
TABLE 1 ______________________________________ Coefficient of Coefficient of Thermal Thermal Metal Expansion (.alpha.) Ceramic Expansion (.alpha.) ______________________________________ Iron 134 .times. 10.sup.-7 /.degree.C. Alumina 70 .times. 10.sup.-7 /.degree.C. Stainless 178 .times. 10.sup.-7 Forsterite 90 .times. 10.sup.-7 SUS 304 Stainless 110 .times. 10.sup.-7 Steatite 80 .times. 10.sup.-7 SUS 430 Nickel 140 .times. 10.sup.-7 Beryllia 75 .times. 10.sup.-7 42 Ni--Fe 67 .times. 10.sup.-7 Kovar 51 .times. 10.sup.-7 ______________________________________
Furthermore, at a glance, it might be supposed that materials which have an approximately equal coefficients, for example, alumina and 42 Ni-Fe alloy described in Table 1, could be used as a combination without causing any problems. However, since 42 Ni-Fe alloy changes to have a high expansion coefficient at a temperature of more than 370.degree. C., a severe thermal strain is caused under conventionally utilized temperatures of several hundred .degree.C. Further, if such strain is repeatedly caused by a heat cycle, the ceramic member or the metal member may be broken, and, e.g., measurement using an oxygen sensor may become impossible.
In order to solve the above-described problem, it has been attempted to modify the adhesive property of a heat-resistant adhesive so as to relieve adhesion of the ceramic member and the metal member. However, such adhesives not only have a problem with respect to the strength of the bond, but also have a disadvantage in that the adhesion interface slides because of differences in the coefficient of thermal expansion to form a large crack(s) between the metal or ceramic member and the adhesive when the heat cycle is repeated, and the air-tightness of the bond deteriorates by the invasion of alien substances into the crack.